This invention relates to image sensor arrays assembled from multiple chips. Many modern control and surveillance systems require imagers for forming signals representing scenes viewed by the imager. Tube-type image sensors such as image orthocons have been largely supplanted by solid-state image devices or sensors for these purposes. Common solid-state image devices include the charge-coupled device (CCD) imager, which is gaining widespread acceptance in home television camcorders. Such CCD sensors for home television use consist of rectangular arrays of 200.times.200, or more, individual light sensors or pixels. CCD arrays are advantageous because of their light weight, ruggedness, low power consumption, relatively great sensitivity to light, and resistance to damage due to light overload. CCD image sensors are also responsive to infrared radiation, and may be used for near-infrared detection or imaging. Cooling improves the infrared operation for some types of detector materials.
The individual light sensor of a CCD sensor array receives light over a certain surface area, and responds to each received photon of light by releasing one or more electrons. The released electrons are integrated during an integration interval to produce individual pixel output signals. The individual sensor output signals are transferred, together with the individual outputs of other similar sensors, to produce the final output signal. The size of the light-receiving area of the individual sensor or pixel, together with the number density of the pixels, is established by the resolution requirements of the imaging system. The sensitivity of the sensors (the minimum light level to which it is desired to respond) is established by the optics of the system, by the integration time, and by the light conversion efficiency of the sensor. Some wavelengths of light are converted into electrons or detected with greater efficiency than other wavelengths. Ordinarily, the individual sensors are roughly square in outline. Such image sensors are described in detail in the text "Charge Transfer Devices" by Se'quin et al., published by Academic Press, Inc. 1975.
Charge transfer devices are manufactured by photolithography, etching and doping in much the same manner as integrated circuits. For a typical individual CCD sensor with dimensions of approximately 60 micrometers (.mu.m) square, a resolution of 1,000 pixels for the array requires a structure which is 60 millimeters (mm) long. Those skilled in the art of manufacturing integrated circuits know that the yield of integrated circuits as a percentage of the total number manufactured is sharply dependent upon the size of the device, because even a single defect attributable to the errors in the crystalline structure of the silicon substrate may render an integrated circuit unusable. In the context of a solid-state imager, such manufacturing defects show up as artifacts in the image. An entire art has grown up which is directed to schemes for compensating for these errors, as for example U.S. Pat. No. 4,481,539 issued Nov. 6, 1984, in the name of Meise et al, so that imperfect imagers may be used commercially.
At the present state of the art, it is difficult to make imagers in which solid-state imager arrays in which more than about one thousand individual sensors are arrayed in a given direction. Consequently, for applications requiring more elements, as for example five thousand sensors arrayed in a line, it is necessary to juxtapose or butt together multiple imager arrays formed on individual dice. It has been found that the image produced by such a compound imager is imperfect in the region of the butt joint.